As the level of technology increases, the options for communications have become more varied. For example, in the last 30 years in the telecommunications industry, personal communications have evolved from a home having a single rotary dial telephone, to a home having multiple telephone, cable and/or fiber optic lines that accommodate both voice and data. Additionally cellular phones and Wi-Fi have added a mobile element to communications. Similarly, in the entertainment industry, 30 years ago there was only one format for television and this format was transmitted over the air and received via antennas located at homes. This has evolved into both different standards of picture quality such as, standard definition television (SDTV), enhanced definition TV (EDTV) and high definition TV (HDTV), and more systems for delivery of these different television display formats such as cable and satellite. Additionally, services have grown to become overlapping between these two industries. As these systems continue to evolve in both industries, the service offerings will continue to merge and new services can be expected to be available for a consumer. Also these services will be based on the technical capability to process and output more information, for example as seen in the improvements in the picture quality of programs viewed on televisions, and therefore it is expected that service delivery requirements will continue to rely on more bandwidth being available through the network including the “last mile” to the end user.
Another related technology that impacts both the communications and entertainment industries is the Internet. The physical structure of the Internet and associated communication streams have also evolved to handle an increased flow of data. Servers have more memory than ever before, communications links exist that have a higher bandwidth than in the past, processors are faster and more capable and protocols exist to take advantage of these elements. As consumers' usage of the Internet grows, service companies have turned to the Internet (and other IP networks) as a mechanism for providing traditional services. These multimedia services include Internet Protocol television (IPTV, referring to systems or services that deliver television programs over a network using IP data packets), Internet radio, video on demand (VoD), live events, voice over IP (VoIP), and other web related services received singly or bundled together.
Multicast is one technique used to distribute IPTV content to users. As used herein, the term “multicast” refers to a broadcast or point-to-multipoint connection which is established between an end user or an end user's device and a content provider or content provider's equipment, e.g., a stream of IP packets which have an address associated with a group of potential recipients. Internet Group Management Protocol (IGMP) is an IP-based control protocol that is used to signal membership of an end station to a multicast group (e.g., associated with an IPTV channel) in a network. So-called IGMP snooping refers to a process for listening to IGMP traffic wherein, e.g., a Layer 2 switch “listens in” on IGMP signaling between hosts and routers by processing layer 3 IGMP packets and compiling group port lists based on snooped IGMP report messages and IGMP leave messages. IGMP snooping may be employed by intermediary nodes in an IPTV network to prune multicast trees in the network to make efficient use of communication resources.
However, such IGMP snooping may cause problems under certain circumstances. For example, if IGMP snooping is used in an IPTV network having an intervening, bridged configuration, the IGMP snooping generates a layer violation between layer 3 (e.g., the IP layer) and layer 2 (e.g., the Ethernet layer) since it is an IP protocol that controls the behavior of multicast streams in Ethernet bridges. This layer violation may cause problems in Provider Bridged networks (PBNs), e.g., 802.1ad type networks and Provider Backbone Bridged networks (PBBNs), e.g., 802.1ah type networks, because IGMP does not take into account additional VLAN information which is introduced with these technologies.
Consider, for example, the IPTV service scenario illustrated in FIG. 1. Therein, two IPTV service providers 10 and 12 operate in the same 802.1ad type network 14 to provide IPTV service. The IPTV service providers 10 and 12 have overlapping multicast IP address spaces which are used to provide IPTV service to various customer sites 20-28. For example, IPTV service provider 10 provides IPTV service to customers 20, 24 and 26 via S-VLAN links 16 through various (unnumbered) Ethernet switches. IPTV service provider 12 provides IPTV service to customers 22, 24 and 28 through S-VLAN links 18. Since the IPTV service providers 10 and 12 have overlapping multicast IP address spaces, these two service providers may have two different IPTV channels (i.e., one apiece) which use the same multicast IP address. If IGMP snooping is used in this network 14 when the same multicast IP address is assigned to two different groups on the two different VLANs, then it will not be possible to distinguish between users joining a first multicast group associated with a channel provided by service provider 10 and users joining a second multicast group associated with a channel provided by service provider 12, which makes IGMP snooping inefficient.
Accordingly, it would be desirable to overcome deficiencies associated with IGMP snooping in certain multicast network topologies, e.g., bridged networks.